A magnetizable composite microsphere having a particle size that ranges from 0.05 to 10 μm is disclosed in U.S. Pat. No. 5,356,713, which has magnetizable nano particles coated with a monolayer of a non-water-soluble dispersing agent at its core, and an outer shell made of cross-linked polymers that enclosed around the magnetizable nano particles. A preparation method thereof is also disclosed, which includes dispersing magnetizable nano particles in a mixture containing ethylene-aromatic monomers, emulsified ethylenically unsaturated monomers, and a dispersing agent added selectively; subsequently adding and allowing an initiator to disperse in the mixture, and finally co-polymerizing the monomers. However, there are still more than 10% of blank microspheres that do not contain magnetizable materials present in the magnetizable microspheres prepared by this method, and the blank microspheres must be separated from the magnetizable microsphere product in a magnetic field. In addition, the magnetizable microspheres prepared by this method have poor monodispersity in particle size. The resulting magnetizable microspheres or aqueous dispersion thereof may be used for immobilizing biologically active substances via adsorption or covalent bonding; such as proteins (antibodies and enzymes), antigens, and medical products. The resulting products may be optimally applied for biological diagnosis and analysis according to the nature of the biologically active substances, such as agglutination assay, radioimmunoassay (RIA), immunoradiometric assay (IRMA), enzyme immunoassay (EIA), and affinity chromatography; or applied as an enzymatic catalyst for biotechnological purposes, and as a carrier for cell cultivation. The disclosure of this U.S. patent is incorporated herein by reference. A magnetizable microsphere that has uniform monodispersity and a particle size that ranges from 0.1 to 5 μm is disclosed in U.S. Pat. No. 5,976,426, which is comprised of a lipophilic polymer matrix and a magnetizable filling. But the magnetizable filling is partially exposed at outside of the lipophilic polymer matrix in the magnetizable microsphere, which limits the application of this magnetizable microsphere for biomedical purposes. The disclosure of this U.S. patent is incorporated herein by reference.